The ability of plants to slough off organs, such as fruit, by an active separation of cells is described by plant physiologists as the process of abscission. Abscission, unaided by mechanical or chemical agents, results from the formation of a starch-filled layer of cells in the area of the fruit rind separating the stem from the fruit. This starch-filled layer is known as the abscission layer. Abscission occurs as the cells in the abscission layer begin to separate, eventually dropping the fruit from the stem. Abscission generally occurs shortly after the fruit has fully matured.
Unfortunately, commercial harvesting of fruit bearing plants very often requires deviation from the natural abscission cycle. Many varieties of fruit bearing plants, such as citrus, reach maturity and are harvested without completion of the abscission cycle. In fact, citrus fruit may actually regreen, i.e., become more tightly attached to the fruit stem, as acceptable maturity standards for eating quality are reached.
When fruit is mechanically harvested without chemical aids and the cells of the abscission layer have not begun to separate or the fruit has begun to regreen, a great deal of force is required to remove the fruit. Often when adequate force to remove the fruit is applied to the fruit or fruit bearing plant, a break or tear may take place and a plug of tissue may be removed from the fruit rind; sometimes the fruit stem is broken, leaving a jagged woody stem attached to the fruit; or the fruit bearing plant itself is injured.
It is apparent that a means of facilitating abscission would not only minimize fruit damage, but also maximize harvest productivity. The quality of the fruit would increase because of less damage, and the yield per tree would increase because of more uniform and complete harvest.
A wide variety of chemicals have been used to regulate the abscission process of fruit bearing plants in attempts to facilitate harvesting. Such chemicals are called, in general terms, harvesting aids or abscission agents. Typical abscission agents are designed and formulated to loosen fruit at the time of harvest. For example, U.S. Pat. No. 3,810,752, granted May 14, 1974, describes the use of pyridine-N-oxides to loosen harvested fruit without significant damage to the rest of the plant. However, previously known abscission agents suffer shortcomings. For example, some agents abscise not only mature fruit, but immature fruit as well, thereby reducing the succeeding year's crop. Many agents abscise leaves as well as fruit also reducing the succeeding year's crop. Finally, many agents cause pre-harvest drop which results in considerable crop loss due to ground-rotting.
Thus, a suitable abscission agent is one which facilitates fruit harvesting without causing abscission of the immature fruit or leaves, or premature ripening. Copending application Ser. No. 602,610, Bednarz and Otten, filed Aug. 7, 1975, now abandoned discloses the use of bis(2-pyridine-N-oxide)disulfides as fruit abscission agents. Copending application Ser. No. 602,335, Otten and Rheinecker, filed Aug. 6, 1975, now abandoned discloses the use of bis(2-pyridine-N-oxide)disfulfones as fruit abscission agents.